This is a continuation of a project to characterize the ultrasonic properties of myocardial tissue in health and disease and to utilize this knowledge in the development of methods to assess regional myocardial perfusion, function, and viability. They have found in previous work that velocity, backscatter, and attenuation of ultrasound vary substantially with the angle of insonification relative to the local arrangement of fibers in the myocardial walls. This anisotropy has largely been ignored, but is thought to be responsible for the drop out of lateral wall echoes in some views of the heart. It is especially important in tissue characterization where subtle changes in ultrasonic properties caused by disease or other abnormalities must be detected in the face of alterations due to angle of incidence. Contrast echocardiography has the potential for assessment of regional myocardial perfusion, but they have found that anisotropy of backscatter and attenuation confounds these measurements as well. In this competitive renewal they propose to: 1) measure the anisotropy of ultrasonic backscatter, attenuation, and velocity in myocardial tissue and delineate the responsible mechanisms; 2) develop strategies for exploiting the knowledge and overcoming the potential difficulties anisotropy presents in echocardiographic imaging, tissue characterization, and contrast echocardiography; and 3) provide baseline knowledge of the anisotropy of myocardial mechanical and elastic properties to improve understanding of cardiac mechanics in normal and diseased hearts.